import sys class VendorImporter: """ A PEP 302 meta path importer for finding optionally-vendored or otherwise naturally-installed packages from root_name. """ def __init__(self, root_name, vendored_names=(), vendor_pkg=None): self.root_name = root_name self.vendored_names = set(vendored_names) self.vendor_pkg = vendor_pkg or root_name.replace('extern', '_vendor') @property def search_path(self): """ Search first the vendor package then as a natural package. """ yield self.vendor_pkg + '.' yield '' def find_module(self, fullname, path=None): """ Return self when fullname starts with root_name and the target module is one vendored through this importer. """ root, base, target = fullname.partition(self.root_name + '.') if root: return if not any(map(target.startswith, self.vendored_names)): return return self def load_module(self, fullname): """ Iterate over the search path to locate and load fullname. """ root, base, target = fullname.partition(self.root_name + '.') for prefix in self.search_path: try: extant = prefix + target __import__(extant) mod = sys.modules[extant] sys.modules[fullname] = mod # mysterious hack: # Remove the reference to the extant package/module # on later Python versions to cause relative imports # in the vendor package to resolve the same modules # as those going through this importer. if sys.version_info > (3, 3): del sys.modules[extant] return mod except ImportError: pass else: raise ImportError( "The '{target}' package is required; " "normally this is bundled with this package so if you get " "this warning, consult the packager of your " "distribution.".format(**locals()) ) def install(self): """ Install this importer into sys.meta_path if not already present. """ if self not in sys.meta_path: sys.meta_path.append(self) names = 'six', 'packaging', 'pyparsing', VendorImporter(__name__, names, 'setuptools._vendor').install()